"Criticism that China initiated a cyberattack is not only groundless, it goes against development of international cooperation on cybersecurity," Hong said.

Hong's comments are nearly identical to those trotted out by the Chinese government whenever security experts speculate that attacks originate from the country.

The evidence of links to Chinese hackers are admittedly tenuous, relying on past accusations by others -- going back to the Aurora attacks that targeted Google and dozens of other Western corporations in late 2009 and early 2010 -- a proven history of hacking activity, and claims that Chinese-language scripts have been found in some of the malware that infected Mitsubishi's servers and PCs.

Yesterday, a U.S.-based spokesman for Mitsubishi confirmed that the company had uncovered a large-scale intrusion that had planted malware on 45 servers and an additional 38 individual PCs in several locations around Japan.

Servers at Mitsubishi's Kobe shipyards, where the company builds diesel-electric submarines and components for nuclear power plants; at the company's Nagasaki shipyards; and at its Nagoya plant, which designs and manufactures missile guidance systems, were among those compromised, the spokesman said.

The attacks were first detected in mid-August, said Mitsubishi, but the company did not go public until Japanese media revealed the intrusion. According to Japanese reports, the government was not informed by Mitsubishi of the attack before this weekend.

The spokesman declined to comment on the origin of the attacks.

Separately, however, Japan's National Police Agency (NPA) today circulated a warning of attacks against government websites based on chatter in Chinese forums.

Messages on those forums last week had called for cyber attacks on the 80th anniversary of the Sept. 18, 1931 "Mukden Incident," when the Japanese military staged an attack against a railroad in the Manchurian region of northern China. The incident was used as a pretext by Japan to invade and occupy Manchuria.

The NPA said that several Japanese government sites were targeted last week, and that the attacks made them difficult to access at times.